The top drive drilling unit of an offshore drilling rig includes a stationary pipe and a rotating pipe disposed in a housing. A caustic and abrasive fluid called mud in the industry flows from the stationary pipe to the rotating pipe at pressures in excess of 5,000 psi. The mud is used to break up rocks and sediment on the ocean floor.
To seal the stationary pipe with respect to the rotating pipe, “V-type” rubber packing material is used. This packing material generates excessive heat and when the packing fails, it can take between one to five hours to replace the packing resulting in costly down time for the drilling operations. Moreover, the top drive unit itself is located about 20 feet up off the drilling platform and workmen must use sledgehammers to replace the packing resulting in a frustrating and hazardous procedure. And, when the packing fails, it fails catastrophically resulting in many barrels of expensive mud being spilled at a cost of a thousand dollars per barrel. Also, the spilled mud must be reclaimed at a significant cost. Worse yet, the packing type seal is inconsistent and sometimes only lasts 5 hours and other times lasts 500 hours.
Thus, the prior art packing seal has plagued the drilling industry with inconsistent seal life, high torque and heat generation, and catastrophic leakage when the seal fails.
Mechanical face seals, known in other industries, have not been used in the drilling industry due to the extreme operating conditions and caustic environment. Also, face seals are usually constructed from brittle ceramic material which, when subjected to high intemal pressures, would crack and fail. Indeed, those skilled in the art of mechanical face seals have studied the drilling industry top drive unit and concluded that conventional mechanical face seals could not be used.
In this invention, a mechanical face seal assembly was designed and tested for a top drive unit and, based on the test results, is expected to give consistent, reliable performance for no less than 500 hours of normal operation.